全文获取类型
收费全文 | 32052篇 |
免费 | 3585篇 |
国内免费 | 1136篇 |
专业分类
化学 | 3087篇 |
晶体学 | 78篇 |
力学 | 1892篇 |
综合类 | 287篇 |
数学 | 5229篇 |
物理学 | 5122篇 |
无线电 | 21078篇 |
出版年
2024年 | 107篇 |
2023年 | 374篇 |
2022年 | 672篇 |
2021年 | 1013篇 |
2020年 | 994篇 |
2019年 | 540篇 |
2018年 | 549篇 |
2017年 | 1159篇 |
2016年 | 1396篇 |
2015年 | 1392篇 |
2014年 | 2326篇 |
2013年 | 2115篇 |
2012年 | 2225篇 |
2011年 | 2140篇 |
2010年 | 1648篇 |
2009年 | 1731篇 |
2008年 | 2010篇 |
2007年 | 2045篇 |
2006年 | 1906篇 |
2005年 | 1603篇 |
2004年 | 1447篇 |
2003年 | 1427篇 |
2002年 | 1007篇 |
2001年 | 808篇 |
2000年 | 671篇 |
1999年 | 557篇 |
1998年 | 463篇 |
1997年 | 344篇 |
1996年 | 316篇 |
1995年 | 315篇 |
1994年 | 249篇 |
1993年 | 181篇 |
1992年 | 132篇 |
1991年 | 143篇 |
1990年 | 86篇 |
1989年 | 68篇 |
1988年 | 73篇 |
1987年 | 52篇 |
1986年 | 50篇 |
1985年 | 67篇 |
1984年 | 43篇 |
1983年 | 32篇 |
1982年 | 36篇 |
1981年 | 27篇 |
1980年 | 47篇 |
1979年 | 45篇 |
1978年 | 26篇 |
1977年 | 35篇 |
1976年 | 36篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Efficient Sequential Quadratic Programming Implementations for Equality-Constrained Discrete-Time Optimal Control 总被引:1,自引:0,他引:1
Efficient sequential quadratic programming (SQP) implementations are presented for equality-constrained, discrete-time, optimal control problems. The algorithm developed calculates the search direction for the equality-based variant of SQP and is applicable to problems with either fixed or free final time. Problem solutions are obtained by solving iteratively a series of constrained quadratic programs. The number of mathematical operations required for each iteration is proportional to the number of discrete times N. This is contrasted by conventional methods in which this number is proportional to N
3. The algorithm results in quadratic convergence of the iterates under the same conditions as those for SQP and simplifies to an existing dynamic programming approach when there are no constraints and the final time is fixed. A simple test problem and two application problems are presented. The application examples include a satellite dynamics problem and a set of brachistochrone problems involving viscous friction. 相似文献
72.
UCINSKI DARIUSZ; JAI ABDELHAQ EL 《IMA Journal of Mathematical Control and Information》1997,14(2):153-174
In this paper, the concept of weak spreadability is introduced.It constitutes an extension of the idea developed by El Jai& Kassara. In the case of linear distributed systems weconsider quadratic control techniques with a conveniently penalizedcriterion which makes the system weakly spreadable. The approachis outlined for a convectiondiffusion system, and theresults of a numerical study are also included to illustratethe main features of the considered problem. 相似文献
73.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
74.
本文介绍了广播发射台利用计算机技术、网络技术、遥控遥测技术、现代测试手段,对设备进行自动化控制与管理;实现设备技术指标自动测试,发射台无人值班、有人留守,建立机器的计算机档案制度,确保安全优质播出的方法和经验。 相似文献
75.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
76.
1 IntroductionSince 1 990 ,chaoticsynchronization[1~ 4] andchaoticcontrolling[5~6] havereceivedagreatdealofattention[7~1 1 ] ,andchaoticsynchronizationisaphenomenonofinterestinfieldsfromelectronicstocommunication[1 2 ] ,andfrombiophysicstoneuro science[1 3] .Ifchaoticsync… 相似文献
77.
Rahul Sarpeshkar Richard F. Lyon Carver Mead 《Analog Integrated Circuits and Signal Processing》1998,16(3):245-274
Low-power wide-dynamic-range systems are extremely hard to build. The biological cochlea is one of the most awesome examples of such a system: It can sense sounds over 12 orders of magnitude in intensity, with an estimated power dissipation of only a few tens of microwatts. In this paper, we describe an analog electronic cochlea that processes sounds over 6 orders of magnitude in intensity, and that dissipates 0.5 mW. This 117-stage, 100 Hz to 10 KHz cochlea has the widest dynamic range of any artificial cochlea built to date. The wide dynamic range is attained through the use of a wide-linear-range transconductance amplifier, of a low-noise filter topology, of dynamic gain control (AGC) at each cochlear stage, and of an architecture that we refer to as overlapping cochlear cascades. The operation of the cochlea is made robust through the use of automatic offset-compensation circuitry. A BiCMOS circuit approach helps us to attain nearly scale-invariant behavior and good matching at all frequencies. The synthesis and analysis of our artificial cochlea yields insight into why the human cochlea uses an active traveling-wave mechanism to sense sounds, instead of using bandpass filters. The low power, wide dynamic range, and biological realism make our cochlea well suited as a front end for cochlear implants. 相似文献
78.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献
79.
80.